User names show up as SIDs in Help Desk portal

We've been rocking along with no problems then today, users can't change their passwords. So far I've heard of two different error messages, both indicating an inability to connect to the domain controller. I've tried my usual tricks (rebooting the server, restarting the service, resetting the service account password) with no luck. Found a KB article that included a suggestion to take the server out of the domain then add it back in, but with no luck. For some reason it appears that my account is the only one that shows up correctly. (See attached.) I'm open to suggestions...